1. Field of the Invention
The present invention relates to an apparatus for enhancing audio quality in audio systems, specifically, an apparatus for providing high quality audio output by a median filter in audio systems.
2. Description of the Prior Art
Sounds are a fundamental way in which people communicate with others. Regardless, if it is voice or music, all are sent by sounds. As new technologies are developed progressively, sounds remain an important way for people to communicate or relax. Products such as audio systems are important products for people to enjoy music and relax. This is especially true of wireless audio systems. The most convenient way to transmit sounds is via air transmission. However, there are also problems with wireless audio systems, and these problems can arise because audio signals are easily influenced by noise during the wireless transmission process. The distorted signals generate popping sounds, subsequently decreasing acoustic fidelity. Therefore, an important research target is to decrease the effect of distorted signals during the wireless transmission process.
Please refer to FIG. 1, which is a functional block diagram of a prior art wireless audio system 10. The wireless audio system 10 includes a transmitting apparatus 12A and a receiving apparatus 12B. The transmitting apparatus 12A is used to transform an audio signal into a radio frequency signal and send the radio frequency signal via air transmission. The receiving apparatus 12B is used to receive the radio frequency signal and transmit the audio signal, which corresponds to said radio frequency signal. The transmitting apparatus 12A comprises two sound inputting devices 14A, 14B, a parallel/serial converter 16, an encoder 18, a burst mode controller (BMC) 19, a modulation module 20, and a transmitting circuit 22. The receiving apparatus 12B comprises a receiving circuit 24, a demodulation module 26, a BMC 28, a decoder 30, a serial/parallel converter 32, two audio conversion devices 34A, 34B, and two speakers 38A, 38B.
In the prior art transmitting apparatus 12A, the sound inputting devices 14A, 14B have a microphone and an analog-to-digital converter (ADC) installed in them. The sound inputting devices 14A, 14B can simultaneously receive two sounds inputted by different audio channels (such as left audio channel or right audio channel). These sounds are recognized as digital data bits (a sample value of each data bit represents an amplitude of the sound) so as to compile sequential digital signals Pa, Pb. The digital signals Pa, Pb are simultaneously transmitted to the parallel/serial converter 16. The parallel/serial converter 16 can encapsulate the two digital signals Pa, Pb of the two sound inputting devices 14A, 14B into a sequential digital signal P1 and output the digital signal P1 to the encoder 18. The encoder 18 adds an error protection code to the digital signal P1. The BMC 19 controls the clock of the digital signal P1 and synchronizes the digital signal P1 so as to form a digital signal P2. The digital signal P2 is transmitted to the modulation module 20. The modulation module 20 modulates the digital signal P2 into an analog baseband signal P3 which is capable of being transmitted via air transmission. The analog baseband signal P3 is sent to the transmitting circuit 22. The transmitting circuit 22 modulates the analog baseband signal P3 into radio frequency signal P4 and transmits the radio frequency signal via air transmission.
After receiving the radio frequency signal P4′ (the corresponding received radio frequency signal relates to P4)transmitted from the transmitting apparatus 12A, the receiving circuit 24 transforms the radio frequency signal P4′ into a baseband signal P5 (the baseband signal P5 corresponds to the original baseband signal P3) and sends the baseband signal P5 to the demodulation module 26. Note that owning to essence of radio transmittion, P4′ may be effected by signal distortion, signal interference, noise, etc. Thus, P4 and P4′ may not be exactly the same. The demodulation module 26 extracts the digital data P6 from the baseband signal P5. The BMC 28 controls the clock of the digital data P6 and synchronizes the digital data P6 so as to generate digital data P7. The digital data P7 corresponds to the original digital data P2. The serial/parallel converter 32 splits the digital data P7 into two digital data Pc, Pd originally identified with the different audio channels. The digital data Pc, Pd corresponding to the digital data Pa, Pb are simultaneously transmitted to audio conversion devices 34A, 34B of different audio channels. The audio conversion devices 34A, 34B are a digital-to-analog converter (DAC). The audio conversion devices 34A, 34B convert the digital signal into analog audio signals Pe, Pf and send the analog audio signals Pe, Pf to the speakers 36A, 36B. The speakers 36A, 36B transmit the acoustic wave corresponding to the analog audio signals Pe, Pf so users are able to hear the sound.
Please refer to FIG. 2, which is a clock diagram of the signals of the audio system 10 shown in FIG. 1. The horizontal axis represents time. The vertical axis of the waveform of the audio signal Pe represents amplitudes. In the transmitting apparatus 12A of the audio system 10, an analog audio wave is sampled as digital signals and transformed into an analog radio frequency signal. This analog radio frequency signal is transmitted via air transmission. When the receiving apparatus 12B receives the analog radio frequency signal, the analog radio frequency signal is reconverted into an analog audio signal. The speakers convert the analog audio signal into an acoustic wave and transmit the acoustic wave so users can hear the sound of the acoustic wave. The single audio channel in audio conversion device 34A will be used as an example. The digital signal Pc (Pc corresponds to the digital signal Pa of the transmitting apparatus 12A) uses the one-by-one sequential data samples to represent the amplitude of the radio frequency analog audio signal Pe waveform on each data sample point. As shown in FIG. 2, a data PS1 (always consisting of eight bits) within the digital signal Pc corresponds to the amplitude of the audio radio frequency signal Pe waveform at time t1. Similarly, another data PS2 within the digital signal Pc corresponds to the amplitude of the audio signal Pe at time t2, and a data PS8 corresponds to the amplitude of the audio signal Pe at time t8. The audio conversion device 34A is used to sequentically transform data within the digital signal Pc into the amplitude of the analog waveform so as to transmit the audio signal Pe.
However, the abovementioned the analog signals are influenced by other radio signals or noise when the analog signals are transmitted via air transmission. The analog signals are influenced by the multi-path effect, meaning that some distortions may occur in the analog signal. When the distorted analog signal is received by the receiving apparatus 12B, the corresponding digital signals Pc, Pd may also have some errors. This erroneous information causes the audio conversion device to emit popping sounds. As shown in FIG. 2, if the data sample PS8 at time t8 has a bit error occurrence, the audio signal Pe at time t8 suddenly appears as a high (or low) impulse so the original smooth audio signal Pe appears to have a suddenly change in waveform. This impulse causes users feel uncomfortable, and decreases the quality of the acoustic fidelity.
In order to prevent the above situation from happening, the prior art technology uses the error protection code to encode the sending signal so as to prevent the error of data. In the transmitting apparatus 12A, the encoder 18 encodes the error protection code in each data of the digital signal P1 according to a coding theorem, so as to form the digital signal P1″. When the receiving apparatus 12B receives the signal with the error protection code, the receiving apparatus 12B transforms the signal into the digital signal P7 and transmits the digital signal P7 to the decoder 30. The decoder 30 corrects the erroneous bits generated during the wireless transmission process according to the error protection code. See FIG. 2, there is a corresponding error protection code in each data of the digital signal P7. For example, a corresponding error protection code e1 is added to the data PS1, and a corresponding error protection code e2 is added to the data PS2, and so on. The decoder 30 corrects the error of the digital signal according to the error protection code within the digital signal P7, so as to obtain the digital signal P8. The digital signal P8 includes the sample value of each data sample. The digital signal P8 is reconverted into an analog audio signal by the serial/parallel converter 32 and the audio conversion devices 34A, 34B.
A primary defect of the prior art is that the prior art wireless audio systems must have complicated encoders and decoders installed. In order to encode the error protection code, the prior art transmitting apparatus 12A must have the encoder 18 installed and the prior art receiving apparatus 12B must have the corresponding decoder 30 installed. Since the encoding algorithms and the decoding algorithms are complicated, the related encoder 18 and decoder 30 must have complex circuits. This is especially true for the decoder 30. The circuit of the decoder 30 is the most complicated of the components in the receiving apparatus 12B. Therefore, the cost and time of design, production, and maintain of the prior art audio system 10 is increased. Additionally, each data becomes longer after having the error protection code added, thereby increasing the data processing load of the audio system 10.